In drill chucks, especially hammer drill chucks, it is desirable to be able to grasp the drill between the clamp jaws so that it is, of course, firmly held rotatably (i.e. without play) and can be fed axially securely and reliably, but is still capable of a comparatively small axial play, in order that the hammer impact provided by a driver apparatus can be most effectively applied to the drill.
In the usual drill chuck with conically shaped clamp jaws which are displaced at an inclination to the chuck axis this can be accomplished only with difficulty.
In such prior art drill chucks there is also a danger of fouling or contamination by borings and cuttings, especially in the spaces around the drill in the drill chuck.
The contamination or drilling detritus can build up until the clamp jaws are jammed shut in their forward position so that the drill chuck must be dismounted often and cleaned. A build-up of drilling dirt will also adversely affect the drilling in other ways including the quality as well as the speed of drilling. The problem is most severe in overhead drilling and where pockets are formed around the jaws at the guide channels therefor.